The present invention relates to information storage techniques and, more particularly, to a novel method for improving the writing behavior of electron-beam-addressed metal-insulator-semiconductor information storage targets.
One form of high-throughput auxiliary memory, useful with large information storage and retrieval systems, is the electron-beam-addressed metal-insulator-semiconductor storage target. The metal-oxide-semiconductor form of this target is described and claimed in U.S. Pat. No. 3,761,895, issued Sept. 25, 1973 and assigned to the assignee of the present invention. The storage target utilizes a semiconductor planar diode structure, typically having an n-silicon layer fabricated upon a p-silicon substrate, with an oxide layer interposed between the n-silicon layer and a conductive (metallic) film. A bit of binary information is stored, at one of a two-dimensional array of possible data sites, in the insulative oxide responsive to impingement thereon of an electron beam, when a first condition of bias between the conductive layer and the n-silicon layer is utilized. The charge stored in the insulative layer is utilized to modulate the signal produced by a reading electron beam, with the modulated signal being produced in the underlying semiconductor diode to achieve a current gain in the target reading mode. The reading gain is susceptible to variations between targets of different processing lots, which undesirable variations appear to be attributable to less-than-optimum storage, in the insulative storage layer, of the charge written into that layer by the writing electron beam. Methods for reducing written charge storage variations, with concurrent reduction of reading gain variations, in a metal-oxide-semiconductor target for use in electron-beam-addressed data storage apparatus, are therefore highly desirable.